Basic carb question

[JG1966]

When I touch the primary accelerator pump while at idle, my engine bogs and almost stalls. 340 with an AED 750 double pumper. Runs terrific with no off idle hesitation. But I've heard that pressing pump shouldn't affect idle if carb is set up perfectly. What -- if anything -- is this telling me, with the fact it almost stalls? I'm too rich? 72 primary, 73 secondary jets with 4.5 power valve. Thanks for help.

 

[oldbee]

Move up the initial timing. We all need more info!

 

[JG1966]

Move up the initial timing. We all need more info!

Initial timing is 20, total 34. All in at 2400. 9-10 hg vacuum. Squirters are 31 primary, 35 secondary. 292/509 cam, 3000 stall, 3.91 rear. I'll try 22 initial, 36 total and see what happens. Engine is happy and running very nice, but I'm wondering if there's even more to be had.

 

[493 Mike]

When you say "touch the acc. pump" do you mean pushing on the pump arm or moving the throttle to open the throttle plates? If the former is the case, that would be normal.
Mike

 

[JG1966]

When you say "touch the acc. pump" do you mean pushing on the pump arm or moving the throttle to open the throttle plates? If the former is the case, that would be normal.
Mike

I mean pushing on the pump arm itself at the spring adjuster. If that's normal, then I heard wrong and that makes me feel better.

 

[lewtot184]

without air your creating a rich condition.

 

[beanhead]

Lewtot is spot-on you're a little rich at idle, or right on the borderline... The engine doesn't like the extra bit of fuel..that would be idle mixture adjustment try turning your idle screws in 1/16 or 1/8 of a turn..(I'm assuming you're just giving the arm a quick little tap, and not putting your weight into it!)

 

[JG1966]

Lewtot is spot-on you're a little rich at idle, or right on the borderline... The engine doesn't like the extra bit of fuel..that would be idle mixture adjustment try turning your idle screws in 1/16 or 1/8 of a turn..(I'm assuming you're just giving the arm a quick little tap, and not putting your weight into it!)

Thanks Bean. I might have given it more than a quick little tap. I'll try it again with that in mind. I already turned screws in about a quarter turn and it seemed to help.

 

[beanhead]

Remember if you push and the idle speeds up you went too lean on the screws...ideally with a slight push the idle should stay pretty constant

 

[Cornpatch MO]

If the accelerator pump arm is set to tight, wouldn't pushing the arm at idle , squirt raw fuel into the venturies, and create instant over rich condition? ................MO